The present disclosure relates generally to electric double layer capacitors, and more specifically to multi-layered electrode architectures having a low equivalent series resistance for incorporation into such devices.
Energy storage devices such as ultracapacitors may be used in many applications such as where a discrete power pulse is required. Example applications range from cell phones to electric or hybrid vehicles. Energy storage devices typically comprise a porous separator and/or an organic electrolyte sandwiched between a pair of carbon-based electrodes. The energy storage is achieved by separating and storing electrical charge in the electrochemical double layer at the interfaces between the electrolyte and the electrodes. Important characteristics of these devices are the energy density and power density that they can provide, which are both largely determined by the properties of the carbon-based electrodes.
Carbon-based electrodes suitable for incorporation into high energy density devices are known. The carbon materials, which form the basis of such electrodes, can be made from natural or synthetic precursor materials. Known natural precursor materials include coals, nut shells, and biomass, while synthetic precursor materials typically include phenolic resins. With both natural and synthetic precursors, carbon materials can be formed by carbonizing the precursor and then activating the resulting carbon. The activation can comprise physical (e.g., steam) or chemical activation.
In order to achieve a high energy density, the carbon materials for incorporation into carbon-based electrodes will have a high specific capacitance. Further, a low equivalent series resistance (ESR) throughout the device is desirable to increase the device's power density. In view of the foregoing, carbon-based electrodes comprising carbon material having a high specific capacitance yet displaying a low equivalent series resistance would be advantageous for incorporation into high power, high energy density ultracapacitors.
According to one embodiment, a multilayer electrode for an electric double layer capacitor comprises a current collector having opposing major surfaces, a fused carbon layer formed over one or both of the major surfaces, a conductive adhesion layer formed over each fused carbon layer, and an activated carbon layer formed over each conductive adhesion layer. The fused carbon layer and the conductive adhesion layer can be continuous or discontinuous layers. The activated carbon may be characterized by its pore size distribution, where pores having a size of ≦1 nm provide a combined pore volume of ≧0.3 cm3/g, pores having a size of from >1 nm to ≦2 nm provide a combined pore volume of ≧0.05 cm3/g, and the activated carbon comprises <0.15 cm3/g combined pore volume of any pores having a size of >2 nm.
Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description present embodiments of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of the invention and together with the description serve to explain the principles and operations of the invention.